1. Field of the Invention
The present invention relates to a technical field involving a driver of a liquid crystal panel of a matrix driving type which adopts transistor driving, metal-insulator-metal (MIM) driving, or the like, and a liquid crystal device and electronic equipment using this driver. More particularly, this invention is concerned with a technical field involving a driver for driving a liquid crystal panel so that images of different aspect ratios can be displayed according to the type of an image signal, a liquid crystal device and electronic equipment using this driver.
2. Description of Related Art
In recent years, liquid crystal devices have been requested to cope with a plurality of different specifications for display in compliance with the demands from markets for displaying a TV picture in a wider screen and for sharing the same specifications for display with computers or the like. However, a dot-matrix type liquid crystal device in accordance with a related art has difficulty in handling a non-image display area in which no picture is displayed and which is produced when corresponding a plurality of specifications for display having different aspect ratios. For example, when an attempt is made to display a screen of an aspect ratio 4:3, which conforms to an existing National Television System Committee (NTSC) standard and a Phase Alternation Line (PAL) standard, being involved in a dot-matrix type liquid crystal device offering a screen of an aspect ratio 16:9 which conforms to a recent high-definition TV standard and an NTSC standard on a wide screen, non-image display areas are created on the right and left sides of the image display field. The non-image display areas are normally blackened. However, when an ordinary shift register is driven for blackening, it is impossible to horizontally scan all pixel electrodes included in the non-image display areas and display them within each horizontal retrace period. Consequently, long adopted is the technique of adjusting the line frequency for a horizontal scan using an external storage device such as a line memory, or the technique of driving a shift register only in the non-image display areas at a high frequency that is 1.5 times to twice higher than the frequency driven in the image display area.
In contrast, when an attempt is made to display a screen with an aspect ratio 16:9 based on the high-definition TV standard or the like in a dot-matrix type liquid crystal device offering a screen with an aspect ratio 4:3 based on the existing NTSC standard or the like, non-image display areas are created above and below the image display area. The non-image display areas are normally blackened. Even in this case, long adopted is the technique of adjusting a line frequency for vertical scanning using an external storage device, or the technique of driving a shift register only in the non-image display areas at a frequency which is higher than the frequency driven in the image display area.
Moreover, Japanese Unexamined Patent Publication No. 9-154086 has disclosed a display device including a device for controlling the horizontal scan so that a signal sent from a sub-video signal processor can be displayed in right and left non-image display areas at the same time. According to this art, since pixels constituting the right and left non-image display areas are scanned at the same time, the time required for scanning the areas is halved.
However, when the foregoing system of driving a shift register, at a frequency higher than the frequency at which the shift register is driven in an image display area is adopted in order to blacken non-image display areas, the shift register must exhibit excellent characteristics. Moreover, there is a problem that since the time required for selecting any pixels in the non-image display areas is shortened, a sufficient contrast ratio cannot be attained. In addition, since the driving frequency becomes high, the power consumption increases. On the other hand, the foregoing system using an external storage device such as a line memory has a problem that not only an increase in cost is invited, but also the design of peripheral circuits or the operational control gets more complex.
According to the art disclosed in Japanese Unexamined Patent Publication No. 9-154086, in order that the pixels constituting the right and left non-image display areas are scanned concurrently, complex circuits such as a sub-video signal processor and video signal switching device must be incorporated in the drive circuit. This makes the configuration of a display device or a control complex. Furthermore, for blackening the right and left non-image display areas, the scan time that is approximately one-half of the scan time required for scanning the pixels in the right and left non-image display areas separately is required.
A technical subject of the present invention is to provide a driver of a liquid crystal panel making it possible to properly blacken non-image display areas using a relatively simple configuration and to display images of various aspect ratios, and a liquid crystal device and electronic equipment including the driver.
For overcoming the aforesaid technical subject, a driver of a liquid crystal panel in accordance with the present invention is a driver for driving a liquid crystal panel that comprises a pair of substrates, a liquid crystal sandwiched between the substrates, a plurality of signal lines which are arranged in a given first direction on the substrate and to which an image signal is supplied, a plurality of scanning lines which are arranged in a second direction orthogonal to the first direction on the substrate and to which a scan signal is supplied sequentially, and a plurality of pixels arranged in the form of a matrix on the liquid crystal side-surface of the substrate, and driven with the image signal and scan signal supplied by the plurality of signal lines and the plurality of scanning lines respectively. The driver comprises an image signal supply unit that includes a first-direction shift register having a plurality of stages, which supplies the image signal sequentially to the plurality of signal lines in a first direction in response to a transfer signal sent sequentially from the first-direction shift register, and a scan signal supply unit that includes a second-direction shift register having a plurality of stages, which supplies the scan signal sequentially to the plurality of scanning lines in a second direction in response to a transfer signal sent sequentially from the second-direction shift register. At least one of the first-direction and second-direction shift registers includes a transfer start control unit for selectively allowing at least two predetermined stages capable of starting transfer among the plurality of stages to start generating a transfer signal.
According to the present invention, there is provided a driver of a liquid crystal panel in which an image signal supply unit supplies an image signal sequentially to a plurality of signal lines in a first direction in response to a transfer signal sent sequentially from a first-direction shift register. Meanwhile, a scan signal supply unit supplies a scan signal sequentially to a plurality of scanning lines in a second direction in response to a transfer signal sent sequentially from a second-direction shift register. As a result, for example, a horizontal scan is carried out according to the transfer signal sent from the first-direction shift register, and a vertical scan is carried out according to the transfer signal sent from the second-direction shift register. Herein, a transfer start control unit included in at least one of the first-direction and second-direction shift registers selectively allows at least two stages capable of starting transfer to start generating a transfer signal. This makes it possible to start, for example, a horizontal scan or a vertical scan at an intermediate position corresponding to a stage capable of starting transfer in at least one of the first and second directions associated with the first-direction and second-direction shift registers. It is therefore possible to display an image in an area contributing to image display, without driving stages preceding the stages capable of starting transfer among the plurality of stages of the first-direction and second-direction shift registers (for example, stages corresponding to the leftmost area or stages corresponding to the uppermost area), that is, stages corresponding to areas not contributing to image display. When the aspect ratio of an image to be displayed is inconsistent with the certain aspect ratio of a screen offered by a liquid crystal panel, an effective image may not be displayed in the uppermost and lowermost areas or the rightmost and leftmost areas. Even in this case, unnecessary scan time for scanning the areas not contributing to image display (non-image display areas) can be eliminated. This obviates the necessity of driving the first-direction and second-direction shift registers at a frequency equal to or higher than a frequency at which the shift registers are driven for scanning the image display area. As a result, the overall circuitry gets simplified and control gets easier. Moreover, a large margin can be ensured for the characteristics of devices constituting a shift register or for power consumption.
According to one aspect of the present invention described above, there is provided a driver of a liquid crystal panel in which the first-direction and second-direction shift registers each include a plurality of transfer signal generation circuits for generating a transfer signal. The transfer start control unit includes a first logic circuit that is connected on a transfer start signal line to which a transfer start signal is supplied and that supplies the transfer start signal to a transfer signal generation circuit on a stage capable of starting transfer and thus allows the transfer signal generation circuit to start generating the transfer signal.
According to this aspect, the first-direction and second-direction shift registers each include a transfer signal generation circuit for generating a transfer signal, for example, a flip-flop. When the first logic circuit, for example, an OR circuit, included in the transfer start control unit applies a transfer start signal to a transfer signal generation circuit on a stage capable of starting transfer, the transfer signal generation circuit starts generating a transfer signal. Thus, it is possible to display an image in an area contributing to image display without driving the transfer signal generation circuits preceding the transfer signal generation circuit on the stages capable of starting transfer.
According to another aspect of the present invention, there is provided a driver of a liquid crystal panel in which at least one of the first-direction and second-direction shift registers includes a transfer stop control unit for selectively allowing at least two predetermined stages, capable of stopping transfer among the plurality of stages, to stop transferring a transfer signal.
According to this aspect, the transfer stop control unit selectively allows at least two stages capable of stopping transfer to stop transferring a transfer signal. For example, horizontal scan or vertical scan can be stopped at an intermediate position corresponding to a stage capable of stopping transfer in at least one of a first and second directions. It is therefore possible to carry out image display in an area contributing to image display without driving stages succeeding the stage capable of stopping transfer among the plurality of stages of first-direction and second-direction shift registers (for example, stages corresponding to the rightmost area and lowermost area), that is, stages corresponding to areas not contributing to image display.
According to this aspect, the first-direction and second-direction shift registers each include a plurality of transfer signal generation circuits for generating a transfer signal. The transfer stop control unit may include a second logic circuit that is connected to a transfer stop signal line to which a transfer stop signal is supplied and that stops a transfer signal sent from a transfer signal generation circuit on a stage capable of stopping transfer according to the transfer stop signal.
Owing to this configuration, the second logic circuit, for example, an AND circuit included in the transfer stop control unit stops a transfer signal sent from a transfer signal generation circuit, for example, a flip-flop corresponding to a stage capable of stopping transfer. Consequently, an image can be displayed in an area contributing to image display without the necessity of driving transfer signal generation circuits succeeding the transfer signal generation circuit corresponding to the stage capable of stopping transfer.
According to another aspect of the present invention described above, there is provided a driver of a liquid crystal panel in which at least one of the first-direction and second-direction shift registers includes a detector for detecting a termination of scan effected with a transfer signal on a given stage. The driver of a liquid crystal panel further comprises a voltage application device for applying a given voltage to pixels constituting non-image display areas outside an image display area defined by an image signal at the same time when a termination of scan is detected.
According to this aspect, when the detector detects a termination of scan effected with a transfer signal on a given stage, the voltage application device applies a given voltage to the pixels corresponding to the non-image display areas at the same time when a termination of scan is detected. The non-image display areas therefore can be, for example, blackened without being scanned.
According to this aspect, the voltage application device may reverse the polarity of the given voltage to be applied to the liquid crystal portions of the pixels according to the image signal at intervals of a given period.
In this case, the liquid crystal portions of the non-image display areas can be driven while the polarity of an applied voltage is reversed for each vertical scan period such as a field or frame or for each scanning line (row). Deterioration of the liquid crystal portions of the non-image display areas derived from application of a DC voltage can be prevented. In particular, flickers can be prevented by reversing the polarity of the applied voltage for each scanning line.
According to another aspect of the present invention, there is provided a driver of a liquid crystal panel in which the image signal supply unit includes a switching device that when driven to conduction according to a transfer signal generated by the first-direction shift register, supplies the externally-input image signal sequentially to the plurality of signal lines.
According to this aspect, a switching device, for example, a thin-film transistor (TFT) to be driven to conduction according to a transfer signal generated by the first-direction shift register, is used to supply an externally-input image signal sequentially to the plurality of signal lines. The switching device is used to sample the externally-input image signal, and a transfer signal generated by the first-direction shift register is used as a driving signal used to drive a sampling circuit, whereby scan in a first direction can be achieved.
According to another aspect of the present invention, there is provided a driver of a liquid crystal panel in which at least one of the first-direction and second-direction shift registers includes a selector for selecting one of the stages capable of starting transfer according to the size of a display image indicated by the image signal.
According to this aspect, the selector selects one of the stages capable of starting transfer according to the size of a display image indicated by an image signal for, for example, NTSC-conformable display, NTSC on wide screen-conformable display, or PAL-conformable display. A scan can be automatically started at a position suitable for the type of an externally-input image signal.
According to an aspect of the present invention in which the transfer stop control unit is included, at least one of the first-direction and second-direction shift registers may include a selector for selecting one of the stages capable of stopping transfer according to the size of a display image indicated by the image signal.
According to this aspect, the selector selects one of the stages capable of stopping transfer according to the size of a display image indicated by an image signal for, for example, a NTSC-conformable display, a NTSC on wide screen-conformable display, or a PAL-conformable display. Consequently, a scan can be stopped at a position suitable for the type of an externally-input image signal. When both the selector for selecting one of the stages capable of starting transfer and the selector for selecting one of the stages capable of stopping transfer are included, needless to say, a scan can be achieved automatically in a manner most suitable for the type of an externally-input image signal.
According to another aspect of the present invention, there is provided a driver of a liquid crystal panel in which the image signal supply unit and scan signal supply unit are each realized with an integrated circuit that is arranged on a first substrate in the perimeter of an image display area defined by the plurality of pixels.
According to this aspect, the image signal supply unit and scan signal supply unit, each realized with an integrated circuit arranged on the first substrate in the perimeter of the image display area, preferably scan the image display area two-dimensionally.
According to the present invention, there is provided a liquid crystal device in which the driver of a liquid crystal panel in accordance with the present invention and the liquid crystal panel are included for overcoming the aforesaid technical subject.
According to the present invention, since the liquid crystal device includes the aforesaid driver of a liquid crystal panel in accordance with the present invention and the liquid crystal panel, while non-image display areas can be blackened properly using a relatively simple configuration, images of various aspect ratios can be displayed.
Furthermore, the electronic equipment in accordance with the present invention is characterized in that the aforesaid liquid crystal device in accordance with the present invention is included for overcoming the aforesaid technical subject.
According to the present invention, there is provided electronic equipment in which, since a liquid crystal device in accordance with the present invention is included, various electronic equipment including a liquid crystal projector, personal computer, and pager which can display images of various aspect ratios in a screen using a relatively simple configuration can be realized.